AB Siwertell of Sweden custom designs and builds ship unloaders that can discharge a wide variety of materials from dry bulk carriers. The company is represented in the United States by Salwico, Inc. of Hoboken, N.J. Compared with pneumatic systems, the Siwertell unloader offers additional features such as: considerably lower power requirement; reduced maintenance and cost for air filters; and ability to handle a wider range of materials.
Free-flowing materials that have well-defined angle of repose are unloaded easily by the Siwertell system. These include granules such as grains, fertilizers, nuts, and soy beans, and particles such as alumina, rock phosphate, and soda ash. The system also handles materials that can form steep-angled banks and hard crusts and for which digging power is essential. Examples are powders such as cement, flour, lime, and potato starch; granules such as pellets; and particles including bauxite, coal, coke, salt, sulphur, and wood chips.
The Siwertell screw conveyor transports the material vertically to the boom, where it is discharged into a horizontal screw conveyor between the outer end of the boom and the center of the slewing tower, from which it is fed down through the slewing ring. From this point, transportation is arranged to suit local requirements. Capacity range is normally 100 to 1,000 tons per hour, but higher capacities can also be economical, depending on the material handled and the size of the ships. Being a closed system, it presents no air pollution problems when fine powders are handled.
A Siwertell ship unloader delivered to Rinker Materials Corporation in Port Canaveral, Fla. has a capacity of 600 tons per hour (cement), is operated from a portable controller, and can unload ships of up to 30,000 dwt.
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